The present invention relates to the treatment of patients by means of extracorporally produced shockwaves, particularly under utilization of contact-free lithotripsy; and more particularly the invention relates to lithotripters which include in each instance a focussing shockwave source, a patient's rest, and equipment for locating concrements in the body of human beings.
Equipment of the type to which the invention pertains generally is, for example, disclosed in German patent application 39 15 382.7 (equivalent to U.S. Pat. No. 5,092,721). The lithotripter in this publication is associated with a locating arm at the therapeutic head. The term "locating arm" is used here for describing a holder for transducers or the like which are provided for finding a concrement using, e.g. ultrasonic equipment. The therapeutic head is the source for carrying out lithotripsy, i.e. for producing focussed shockwaves.
The reference above disclose a geometric and physical relation in between a locating arm and a transducer mounted on the locating arm, and a so-called therapeutic focus as established by the shock-wave source. That relation between is variable and adjustable and can be tracked by means of appropriate measuring equipment.
The requirements as far as the mechanics of this device are concerned are considerably smaller than in the case of a locating arm that has no fixed connection in relation to the therapeutic head. However, it was found that this advantage is considerably diminished owing to the problems that result from the relative motion of the arm once it is fixed in relation to the patient. In addition, there is a problem that a kidney stone, e.g. which is imaged by way of an ultrasonic image, may be "lost" and still furthermore there is a problem of danger to the patient through collision between the body of the patient and the equipment.
Another possibility is given in German petty patent utility model 8800985 wherein it is disclosed that there is a locating arm affixed to the patient rest. This particular arrangement has the advantage that once the kidney stone has been located the arm can be fixed in some fashion to the surface of the patient without changing the position of the arm relative to the patient once the patient rest has been moved relative to the therapeutic head. The therapeutic head in turn remains coupled and the image portion as displayed in not varied; hence there is no danger of collision.
However, this arrangement has the disadvantage that the position of the therapeutic focus relative to the rest has to be determined and redetermined and adjusted, which is deemed a disadvantage. Aside from the inaccuracies in the acquisition of these parameters there is another possibility for error, namely any possible deformation of the patient rest under the load of the patient's weight which from that point of view remains unforeseeable but may introduce a locating error as regards the relation between the locating arm and the therapeutic head.
Affixing the locating arm for the ultrasonic locating transducer to the patient's rest is definitely disadvantageous as compared with connecting that locating arm to the therapeutic unit. The accuracy that is needed will suffer; on the other hand an arm affixed or connected to the therapeutic unit is more difficult to control during positioning. Moreover, developments in the past have led to a highly accurate transducer positioning arm that is realizable only by means of a very complex and usually rather heavy and unwielding mechanism. U.S. Pat. No. 4,669,438, corresponding to German patent 3427001 C1, discloses a lithotripter with a locating device that is affixed to a patient's rest; a second locating device is connected to the therapeutic head (FIG. 2 of that reference) but this duplication is relatively unwieldy in its own right. Moreover the range of permissible and possible motion of the second locating device is quite limited; there are just too many pieces of equipment in too limited a space.
For further information on the kinematics see U.S. patent applications, Ser. Nos. 513,612 and 513,613 now U.S. Pat. No. 5,078,124.